Subsequent to the drilling of an oil or gas well, it is common to install a production casing and to perforate the casing in the area of the formation from which production of oil or gas is to be extracted. At times, either prior to the extraction of oil or gas from the formation through the perforation zone or subsequent to a period of oil or gas production, it may become beneficial or, indeed, necessary to stimulate the flow of oil or gas from the formation. Stimulation may be required as a result of a blockage which has occurred in a portion or all of the perforations in the casing or as a result of the natural decline in production as a result of the extraction of oil or gas from the formation. It is desirable to have the capability of directing the stimulation fluid, which may be water, steam or an acid solution, through selected casing perforations.
In the past, this has been accomplished by using tools having spaced packers which seal off below and above the perforations through which the appropriate work over fluid is to be injected. Then, a fluid under pressure is ejected out of the tool and into the casing area which has been packed off, thereby directing the fluid out of the casing through selected perforations.
Prior art devices have been generally of two types. One type has used cup type packers incorporating seals which are biased outwardly against the casing wall during all movement of the tool in the casing. As can be appreciated, this type of tool introduces additional wear and the possibility of damage to the packers in view of the continuous contact of the packers with the casing wall. Additionally, other operations, such as the use of the tool during clean out of the bottom of the well, are made more difficult in that fluid injected between the tool and the well casing is restricted by the packers.
A more recently developed washing tool incorporates packers which are expanded after the tool is in place. Subsequent to expansion of the packers, the cleaning or fracturing fluid is then discharged from the tool through the perforations isolated between the packers. While this device has some advantages over the prior cup type packer tools, the tool is unnecessarily complicated as a result of valving which controls the sequences of packing off the section of the casing prior to ejection of fluid into the perforation zone of the casing.